1. Field of the Invention
The present invention relates in general to electrochromic devices and, more particularly, to an electrochromic device having one or more slow-diffusing electroactive materials and an electron shuttle which serves to decrease the switching time of the electrochromic device relative to the same without such an electron shuttle.
2. Background Art
Electrochromic devices have been known in the art for several years. Furthermore, the utilization of one or more slow-diffusing electroactive materials in the medium of electrochromic devices has been disclosed in U.S. application Ser. No. 10/054,108 entitled “Controlled Diffusion Coefficient Electrochromic Materials For Use In Electrochromic Mediums and Associated Electrochromic Devices.” While the above-identified U.S. Application discloses many benefits of utilizing one or more slow-diffusing electroactive materials, the switching times of associated electrochromic devices can be adversely affected and, in some circumstances, problematic for commercial applications.
In addition, U.S. Pat. No. 6,445,486 B1 entitled “Electroactive Materials And Beneficial Agents Having A Solublizing Moiety” discloses incorporating a solublizing moiety with electroactive materials to, in turn, enhance solubility of the electroactive material in a preferred solvent. While utilization of a solublizing moiety with electroactive materials beneficially affects the solubility characteristics of electroactive material, the solublizing moiety can adversely affect the diffusion characteristics of the same.
When an electrochromic device is in its normal rest state, (i.e. when a zero-electrical potential difference is applied) the electrochromic device is said to be in a high-transmission state. In the high-transmission state the cathodic material (i.e. the material to be reduced at the device cathode) and anodic material (i.e. the material to be oxidized at the device anode) are neither reduced nor oxidized, respectively. Typically, no coloration or very low coloration characterizes the high-transmission state, but occasionally an intentional tinting of the high-transmission state is desirable.
When a sufficient electrical potential difference is applied across the electrodes of a conventional electrochromic device, the electrochromic medium becomes colored due to oxidation of the anodic material and reduction of the cathodic material. Specifically, the anodic material is oxidized by donating one or more electrons to the anode, and the cathodic material is reduced by accepting one or more electrons from the cathode. For most commercially available electrochromic devices, application of this electrical potential difference and subsequent coloration of the medium results in reduction of transmission of the device. The reduced transmission state of the device is typically referred to as the low-transmission state.
When the electrical potential difference is removed or sufficiently reduced, the oxidized anodic material and reduced cathodic material return to their zero-potential or unactivated state, and in turn, the device returns to a high-transmission state. The complete transitioning of an electrochromic device from high to low to high transmission states is referred to as a cycle.
In the case of automotive applications of electrochromic devices, specifically electrochromic mirrors, the speed at which the device transitions from a high-transmission state to a low-transmission state, and back again is very important for driver and passenger safety. For example, if the transition to a low-transmission state is too slow, the driver may be distracted or blinded by reflection of rear-approaching headlights. Conversely, if the mirror is too slow to revert to the high-transmission state the driver may not be able to see possible hazards in the rear view. Currently available electrochromic devices switch at acceptable speeds which do not pose safety risks. However, as was previously discussed, emerging technologies, particularly those involving automotive mirror applications which utilize one or more slow-diffusing electroactive materials, can present problematic switching times.
It has now been surprisingly discovered that incorporation of one or more anodic and/or cathodic electron shuttles as disclosed herein serves to decrease switching time of an associated electrochromic device relative to the same without the electron shuttle(s).
It is therefore an object of the present invention to provide an electrochromic device having one or more slow-diffusing electroactive materials and an electron shuttle that remedies the aforementioned detriments and/or complications associated with the incorporation of one or more slow-diffusing electroactive materials into the medium of an electrochromic device.